Volcanoes form at three main types of boundaries: convergent plate boundaries, divergent plate boundaries, and at hot spots within tectonic plates. Magma rises from below the Earth's surface through vents or fissures to erupt as volcanoes. There are three main types of volcanic cones - shield volcanoes which have low-angle eruptions of basaltic lava, cinder cones which are small and steep with explosive eruptions, and composite or stratovolcanoes which are large mountains composed of hardened lava and tephra from alternating eruptions. Volcanic eruptions can produce hazards such as lava flows, tephra falls, lahars, pyrocl

1. VOLCANOES

2. Launch Lab
• Take one beaker (containing water and oil)
and salt cup
• Sprinkle salt into the beaker in one spot for
five seconds
• Observe
1.Which component of your model represents
magma?
2.What happened to the oil before and after you
added the salt?
3.What do you think causes “magma” (oil) to
rise?

3. Volcanism
• Movement of magma toward or onto
the Earth’s surface
***magma is less dense than surface so
it pushes its way up

4. Volcanoes
• http://mass.pbslearningmedia.org/resource/i
dptv11.sci.ess.earthsys.d4kvol/volcanoes/

5. Where they form….
1. Convergent Boundaries
2. Divergent Boundaries

6. Where they form….
3. Hot Spots

7. Hot Spots
• Magma comes to the surface from
within a plate (not at a boundary)
that continues to move over spot
producing lava
Hawaiian
Islands
Galapagos
Islands

8. How Hawaii was formed ….
• http://mass.pbslearningmedia.org/resource/nat08.

9. All three types

10. Parts of a Volcano
• Volcanic cones – piles of volcanic material
built up around vent
• What you see on the surface and call
volcanoes

11. Parts of a Volcano
• Lava = Magma on earth’s surface
• Tephra = fragments of volcanic
rock blown into atmosphere
• Conduit = tube-like structure lava
travels through to create a vent

12. Parts of a Volcano
•Vent = opening in earth’s surface
where magma flows through
•Fissure = linear crack which lava
flows out

13. vent
fissure

14. Anatomy of a Volcano

15. Crater vs. Caldera
• Crater = bowl-shaped depression
at top of vent; formed when
material is blown from vent
during explosions
• Caldera = large basin
shaped depressions
formed either by
explosions or cones
collapsing

16. Types of Volcanoes
• http://www.pbs.org/wgbh/nova/earth/meet-volcan

17. Three types of
Cones (volcanoes)
1. Shield cone
- largest type
-quiet eruptions where
lava slowly flows out
- basaltic lava

18. Basaltic lava flows into ocean
• http://mass.pbslearningmedia.org/resource/b
f10.sci.ps.earth.stormsea/stormy-seas/

19. Basaltic Lava
On land:
pahoehoe – thin lava with wrinkled
hardened texture
aa – sharp chunks of lava that form
when lava continues to flow
underneath cooling lava

20. Basaltic Lava
In Ocean:
pillow lava – shape of cooled lava
that escapes fissures of midocean ridges

21. Three types of Cones
(volcanoes) cont…
2. Cinder cone
- made up of solid fragments
- steep slopes
rarely high
very
explosive
- Smallest kind
- Forms on edge of
Other cones

22. Three types of Cones
(volcanoes) cont…
3. Composite Cone (stratovolcanoes)
- alternating hardened lava and tephra
- lava flows clog vent and cause eruption
of tephra then lava flows cause clog
again
- develop into high volcanic mountains
- Mt. St. Helen’s, Mt. Pinatubo, Mt. Rainier

24. Mt. St. Helens

25. Mt. St. Helens
• http://mass.pbslearningmedia.org/resource/i
dptv11.sci.ess.earthsys.d4kmsh/mount-sthelens/

26. Other hazards from eruptions

27. Volcanic Rock Fragments
• Volcanic bombs – rounded or spindle shape
tephra particles caused by lava spinning
through air
• Volcanic blocks – largest kind of tephra –
some as big as houses

28. Lahars
• Lahars - mudflows made of pyroclastic
material, mud, and water
– Very destructive
– Dense as concrete

29. Mt. Pinatubo
• http://mass.pbslearningmedia.org/resource/e
ss05.sci.ess.earthsys.lahar/mount-pinatubothe-aftermath-of-a-volcanic-eruption/

30. Pyroclastic flows
• Pyroclastic flows - Rapidly moving clouds
of tephra mixed with hot, suffocating gases
(sulfuric acid)

33. Predicting Volcanoes
1. Seismographs
2. measuring gases given off –
sulfur dioxide (SO2)
3. study past history of volcanoes
4. bulging of volcanic slopes
•
http://mass.pbslearningmedia.org/resource/ess05.sci.ess.earth
sys.pinatubo/mount-pinatubo-predicting-a-volcanic-eruption/

34. Extraterrestrial
Volcanism
Many planets &
moons in the solar
system were and
are volcanically
active

35. Extraterrestrial
Volcanism
The Moon
Covered by Basaltic flows;
no longer active; however,
no evidence of plate tectonic
activity

36. Extraterrestrial
Volcanism
Mars
Numerous volcanoes &
features; biggest one is
a shield volcano called
Olympus Mons

37. Extraterrestrial
Volcanism
IO
Moon on Jupiter; shows 9
active volcanoes erupting on
Io
http://mass.pbslearningmedia.org/
resource/flbe12.sci.ess.eiu.iovolca
no/io-and-volcanism/

39. Yellowstone
• http://mass.pbslearningmedia.org/resource/n
vdv.sci.earth.yellowvolc-1/volcanism-atyellowstone/